1. Field of the Invention
The present invention relates to a method and a system for preventing incontinent liquid drip, in which any incontinent liquid drip of a coating liquid toward a semiconductor wafer can be reliably prevented by controlling the flow rate of the coating liquid, for example, when the supply of the coating liquid to be applied to the semiconductor wafer is stopped.
2. Description of the Related Art
The uniformity of the film thickness of the coating liquid (resist liquid) is an important factor of the product quality as the pattern becomes fine in the production steps for the semiconductor wafer. Therefore, the so-called incontinent liquid drip, in which a minute amount of coating liquid drips toward the semiconductor wafer from a nozzle as a supply port for the coating liquid when the supply of the coating liquid to the semiconductor wafer is stopped, is prevented, because of the following reason.
That is, when the supply of the coating liquid to the semiconductor wafer is stopped, if the incontinent liquid drip occurs to drip the minute amount of coating liquid from the nozzle, then the uniformity of the thickness of the film formed on the semiconductor wafer is deteriorated, resulting in a defective product.
As shown in FIG. 21, a coating liquid supply system 1 concerning the conventional technique comprises a coating liquid supply source 2, an opening/closing valve 3 connected to the coating liquid supply source 2, and a suck back valve 4. A coating liquid-dripping apparatus 7, which is provided with a nozzle 6 for dripping a predetermined amount of coating liquid to a semiconductor wafer 5, is connected to the output side of the suck back valve 4. The opening/closing valve 3 functions to switch the supply state and the supply stop state of the coating liquid for the suck back valve 4 in accordance with the valve-opening or valve-closing action. The suck back valve 4 functions to suck the coating liquid existing in the nozzle 6 in accordance with the action of negative pressure so that the incontinent liquid drip from the nozzle 6 toward the semiconductor wafer 5 is prevented.
In the conventional technique, a skilful operator works to prevent the incontinent liquid drip of the coating liquid from the nozzle 6 toward the semiconductor wafer 5 by finely adjusting the operation timing and the operation speed of the opening/closing valve 3 and the suck back valve 4 while visually observing the incontinent liquid drip phenomenon at the forward end of the nozzle 6.
However, in the case of the coating liquid supply system 1 concerning the conventional technique, the incontinent liquid drip is prevented by delicately adjusting the operation timing and the operation speed of the opening/closing valve 3 and the suck back valve 4 while the skilful operator visually observes the incontinent liquid drip phenomenon at the forward end of the nozzle 6 on the basis of the experience and the intuition. Therefore, an inconvenience arises in that if an unexperienced operator works, then it is difficult to perform the adjustment, or a lot of time is required to perform the adjustment.
As the semiconductor wafer becomes to have a large size, a surfactant is used and added to the coating liquid in order to improve the dispersion performance of the coating liquid on the wafer surface. For this reason, the surface tension of the coating liquid is lowered, and the incontinent liquid drip tends to occur more frequently. It is demanded to prevent the incontinent liquid drip more reliably and stably.
If it is intended to prevent the incontinent liquid drip by improving the control accuracy of the suck back valve, other inconveniences occur as follows. That is, the cost of the suck back valve is increased, and the operation for adjusting the suck back valve is complicated.